task: https://stepik.org/lesson/24460/step/10?unit=6766

solution.py

#!/bin/python3

class tree():

    def add(self, variable):
        self.variables.append(variable)

    def create(self, namespace):
        namespace.parent = self
        self.children.append(namespace)

    def get(self, item):
        if item not in self.variables:
            parent = self.parent
            while parent:
                if item in parent.variables:
                    return parent.name
                parent = parent.parent
            return None
        return self.name

    def __init__(self, name, parent=None):
        self.name = name
        self.parent = parent
        self.variables = []
        self.children = []

    def __str__(self):
        return f"parent: {self.parent}, name: {self.name}, vars: {self.variables}, children: {self.children}"


global_tree = tree('global')


def bfs(item, start=global_tree):
    queue = [start]
    while queue:
        current_tree = queue.pop(0)
        if item == current_tree.name:
            return current_tree
        for child in current_tree.children:
            queue.append(child)
    return None

def create(name, parent_name):
    parent = bfs(parent_name)
    parent.create(tree(name))

def add(namespace, item):
    parent = bfs(namespace)
    parent.add(item)

def get(namespace, var):
    parent = bfs(namespace)
    print(parent.get(var))

if __name__ == '__main__':
    iterations = int(input())
    for _ in range(iterations):
        command, arg1, arg2 = input().split()
        if command == 'add':
            add(arg1, arg2)
        elif command == 'create':
            create(arg1, arg2)
        elif command == 'get':
            get(arg1, arg2)
        else:
            print('undefined command')